1. Field of the Invention
The present invention relates to a seat slide device which is optimally applied for an automotive vehicle, and specifically to a powered seat slide device with a walk-in mechanism by means of which a space necessary for getting on and out the car is satisfactorily obtained.
2. Description of the Prior Art
As is generally known, a conventional automotive seat slide device has a telescopically extendable guide rail structure for each side of the seat assembly. The telescopically extendable guide rail structure is interposed between the seat cushion and the floor panel of the car. The telescopically extendable guide rail structure is generally comprised of an upper slidable guide rail firmly secured to a respective side portion of the base plate of the seat and a lower stationary guide rail rigidly mounted on the floor panel. Recently, there have been proposed and developed various powered seat slide devices such as a motor-driven seat slide device. The powered seat slide device includes a guide rail driving unit consisting of a drive motor for example a DC motor and a gear box operably enclosed therein a worm and a worm wheel. The worm has a driven connection with a drive shaft of the motor, while the worm wheel has external threads put into meshed contact with the worm. The guide rail driving unit also includes a screw-threaded shaft rotatably supported by either one of the upper and lower guide rails through bearings at both ends of the one guide rail and a nut member being into threaded engagement with the screw-threaded shaft and fixed to the other guide rail. In general, the screw-threaded shaft has a driven connection with the drive motor through the worm gear box. Rotation of the screw-threaded shaft results in a relative sliding motion of the upper slidable guide rail to the lower stationary guide rail. Thus, the fore-aft position adjustment of the seat is achieved. On more earlier cars, the powered seat slide device employs a so-called walk-in mechanism which is mechanically linked to the slidable upper rail so that the upper rail is interlocked to the lower rail with the walk-in mechanism conditioned in its locked position. In contrast, when the walk-in mechanism is conditioned in an unlocked state, the upper rail is free from the lower rail, so as to permit a relative sliding motion of the upper rail to the lower rail. In two-door type vehicles, the walk-in mechanism usually cooperates with a reclining device in order to ensure a wider space necessary for getting on and out the car through pulling operation of a reclining lever. One such conventional powered seat slide device with a walk-in mechanism has been disclosed in Japanese Second Publication (Tokko Heisei) No. 5-3387.
The powered seat slide device with a walk-in mechanism disclosed in the Japanese Second Publication No. 5-3387 includes an upper slidable guide rail having a C-channel in cross-section, a lower stationary guide rail having a C-channel in cross-section, and a H-shaped intermediate slidable guide rail. The openings of C-channeled upper and lower guide rails oppose to each other, such that two parallel flat rail sections are slidably accommodated in internal spaces defined in the two opposing C-channeled rails. A screw-threaded shaft is rotatably supported by the intermediate guide rail at both ends thereof, while a nut member which is in threaded contact with the screw-threaded shaft is fixed onto the lower stationary guide rail. The screw-threaded shaft has a driven connection with a drive motor in a conventional manner. Therefore, rotation of the screw-threaded shaft results in a relative sliding motion of the intermediate guide rail to the lower guide rail. In the prior-art powered seat slide device described in the Japanese Second Publication No. 5-3387, a walk-in mechanism is provided between the upper slidable guide rail and the intermediate slidable guide rail, in such a manner as to interlock the upper guide rail to the intermediate guide rail. The walk-in mechanism comprises an engaging slot formed in the intermediate guide rail, a locking nail which is arranged on the upper rail so that the locking nail is inserted through a slot formed in the side wall of the upper rail into the engaging slot of the intermediate rail at a predetermined relative position between the upper and intermediate rails, for the purpose of the above-noted interlocking. With the locking nail positioned out of the engaging slot, the upper rail is free from the intermediate rail, while the sliding motion of the intermediate rail to the lower rail is restricted by way of threaded-engagement between the screw-threaded shaft and the nut member. Thus, the upper rail, i.e., the seat cushion can be rapidly moved at the most forward position in the unlocked state of the walk-in mechanism, thereby facilitating getting on and out the car. However, such an intermediate guide rail increases the number of parts of a powered seat slide assembly. Production costs of the powered seat slide assembly may be increased. In addition, the intermediate rail never contributes to lightening of a powered seat sliding device for automotive vehicles. In the above-mentioned prior art, since the additional intermediate guide rail is incorporated into the upper and lower guide rails and the walk-in mechanism is arranged between upper and intermediate rails to mechanically interlock these rails together, the two engaging slots must be machined on the side walls of the upper and intermediate rails. This results in slight reduction of rigidity of the guide rail assembly.